Multilayer composite membranes composed of carbon molecular sieve membranes sandwiched between stacked zeolite nanosheets

Abstract

This study proposes a novel method for fabricating composite membranes with a unique multilayer structure comprising Mobil-type five (MFI) zeolite nanosheets and carbon molecular sieve (CMS) membranes. The proposed fabrication method involves direct solution casting of a nanosheet/polymer composite onto porous alumina supports and subsequent carbonization, thereby eliminating the necessity for intermediate layers, typically required in most conventional supported CMS membranes. The fabricated membranes exhibit clear molecular sieving separation attributes, demonstrating the efficiency of the proposed method in preparing membranes without intermediate layers. Furthermore, the membranes exhibit an intriguing morphological configuration, wherein the CMS layers occupy the interstitial spaces between the stacked zeolite nanosheets. Therefore, compared with conventional CMS membranes without nanosheets, the fabricated CMS membrane with MFI nanosheets contain a significant proportion of sp2 bonded carbon atoms. The distinct physical and chemical structures of the composite membrane considerably improve its stability against structural densification associated with physical aging. A marginal H2 permeance reduction is observed for the 6 and 10 wt% loading samples of the composite membrane after aging for 100 d at 180 °C. Moreover, the H2/CO2 selectivity of the 6 wt% loading sample of the aged membrane increased from approximately 4 to 21, surpassing the upper bound of the corresponding gas pair. Thus, the proposed method can be used for fabricating molecular sieve membranes owing to its advantages such as ease of membrane preparation and gas-separation performance and structural stability enhancements of the fabricated membranes.